Storage tank containment system

ABSTRACT

A storage tank containment system including a cubic-shaped tank having an outer shell having cylindrical walls and an internal cross brace interconnecting the cylindrical walls for the efficient storage and transportation of large quantities of fluid, for example, liquid natural gas.

This application claims the benefit of the provisional patentapplication Ser. No. 60/854,593 for a STORAGE TANK FABRICATION, filed onOct. 26, 2006. This claim is made under 35 U.S.C. §119(e); 37 C.F.R.§1.78; and 65 FR 50093.

FIELD OF THE INVENTION

The invention generally pertains to storage tanks and more particularlyto storage tanks for fluids including liquids and gases.

BACKGROUND

Industrial storage tanks used to contain liquids or compressed gases arecommon and are vital to industry. Storage tanks may be used totemporarily or permanently store fluids at an on-site location or may beused to transport the fluids over land or sea. Numerous inventions inthe structural configurations of fluid storage tanks have been made overthe years. One example of a non-conventional fluid storage tank having acube-shaped configuration and support structure is found in U.S. Pat.No. 3,944,106 to Thomas Lamb, the entire contents of the patent areincorporated herein by reference.

There has been a progressive demand for the efficient storage and longdistance transportation of fluids such as liquid natural gas (LNG),particularly over seas by large ocean-going tankers or carriers. In aneffort to transport fluid such as LNG more economically, the holding orstorage capacity of such LNG carriers has increased significantly fromabout 26,000 cubic meters in 1965 to over 200,000 cubic meters in 2005.Naturally, the length, beam and draft of these super carriers have alsoincreased to accommodate the larger cargo capacity. The ability tofurther increase the size of these super carriers, however, haspractical limits in the manufacture and use.

Difficulties have been experienced in the storage and transportation offluids, particularly in a liquid form, through transportation by oceancarriers. A trend for large LNG carriers has been to use largeside-to-side membrane-type tanks and insulation box supported-typetanks. As the volume of transported fluid increases, the loads on thetank containment walls increases significantly. These membrane andinsulation type of tanks suffer from disadvantages of managing the“sloshing” movement of the liquid in the tank due to the naturalmovement of the carrier through the sea. As a result, the effectiveholding capacity of these types of tanks has been limited to either over80% full or less than 10% full to avoid damage to the tank lining andinsulation. The disadvantages and limitations of these tanks areexpected to increase as the size of carriers increase.

The prior U.S. Pat. No. 3,944,106 tank was evaluated for containment ofLNG in large capacities, for example, in large LNG ocean carriersagainst a similar sized geometric cube tank. It was determined that the'106 tank was more rigid using one third the wall thickness of thegeometric cube. The '106 tank further significantly reduced the velocityof the fluid, reduced the energy transmitted to the tank and reduced theforces transmitted by the fluid to the tank causing substantially lessdeformation of the tank compared to the geometric cubic tank.

It was further determined, however, that the '106 configured tank didnot prove suitable to handle large capacities of LNG in a large LNGcarrier environment.

Therefore, it would advantageous to design and fabricate storage tanksfor the efficient storage and transportation of large quantities offluids such as LNG across land or sea. It is further desirable toprovide a storage tank that is capable of being fabricated in ship yardsfor large tankers that further minimizes the number of components andminimizes the different gages or thickness of materials that are neededfor the tank. It is further advantageous to provide a modular-type tankdesign which facilitates design, fabrication and use in the field.

SUMMARY

The inventive storage tank containment system includes a six-sidedgenerally cube-shaped outer shell and an internal cross-braceinterconnecting at least five of the six sides of the storage tank.

In one example, the outer shell of the tank includes twelvesubstantially identical cylindrical-shaped walls interconnected to oneanother at opposing edges. The outer shell further includes eightspherical-shaped end caps closing the corners of the cube-shaped tank.The internal cross brace structurally reinforces the cylindrical wallsand further distributes the loads due to containment and movement of thefluid contents.

In an alternate example, a different internal cross brace is used whichincludes a structurally reinforced column, angularly opposed sidebrackets and end reinforcements.

In another alternate example, cross brace side extensions are used withthe internal cross brace along with a base plate to transfer and supportthe loads of the tank to the fore, aft and transverse bulkheads and tanktop of the cargo hold, for example, in a large ocean carrier.

The particular design of the tank base support and extensions providesadvantages to support the weight of the tank and its contents and tolaterally position the tank center at the same location as the tankthermally contracts, for example, as the low temperature liquid isloaded into it. Above each slot, a locking plate may be provided toprevent the extension from moving out of the mounting slot in a ship dueto motion in heavy seas.

Other applications of the present invention will become apparent tothose skilled in the art when the following description of the best modecontemplated for practicing the invention is read in conjunction withthe accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The description herein makes reference to the accompanying drawingswherein like reference numerals refer to like parts throughout theseveral views, and wherein:

FIG. 1 is schematic perspective view of an example of a stand alone tankcontainment system;

FIG. 2 is partial schematic of the tank in FIG. 1 with the exemplaryspherical end caps removed showing part of the internal tank;

FIG. 3 is a perspective view of one cylindrical wall component of thetank in FIG. 2;

FIG. 4 is a partial exploded view of an alternate example of the tankshown in FIG. 2 where the spherical ends caps are deleted;

FIG. 5 is a perspective view of one example of an internal cross brace;

FIG. 6 is a perspective view of an alternate example of an internalcross brace;

FIG. 7 is a schematic perspective view of an alternate storage tankcontainment system with an alternate cross brace and cross brace sideextensions;

FIG. 8 is a schematic perspective view of the bottom side of the tankshown in FIG. 7;

FIG. 9 is a partial cut-away side view of the alternate tank and crossbrace shown in FIG. 7;

FIG. 10 is a schematic side view of the tank shown in FIG. 7 installedin a marine vessel cargo hold area;

FIG. 11 is an enlarged view of a portion of FIG. 10;

FIG. 12 is a partial top view of the storage tank shown in FIG. 10 asviewed from direction A in FIG. 11;

FIG. 13 is a schematic side view taken from the view of arrow B in FIG.12 showing the side extension positioned in a slot in a cargo hold;

FIG. 14 is a perspective view of an alternate example of the sideextensions shown in FIG. 7;

FIG. 15 is a schematic perspective view of an alternate internal crossbrace; and

FIG. 16 is a schematic side view of an example of an ultra-large LNGcarrier with four storage tanks positioned in respective cargo holds.

DETAILED DESCRIPTION

Several examples of the storage tank containment system in explementaryuses are shown in FIGS. 1-16. Referring to FIGS. 1 and 2, thecontainment system includes a storage tank 10 having a generallysix-sided cubic configuration. Tank 10 includes twelve independent,substantially identical cylindrical walls 30. The cylindrical walls 30are arranged to include four vertical cylindrical walls 34 and eighthorizontal cylindrical walls 40 generally arranged and configured asshown in FIG. 2. The cylindrical walls 30 form an outer shell of tank 10having six sides including a top side 14, bottom side 18 and fourintermediate sides 20. The combined cylindrical walls define a interiorstorage chamber 66 for containment of materials or preferably fluidsincluding liquids and/or gases maintained at or above atmosphericpressure.

As best seen in FIG. 3, each cylindrical wall 30 includes acylindrical-shaped center portion 46 having first ends 50, adjacentedges 52 and second ends 56. As shown in FIG. 2, each cylindrical wall30 interconnects with four adjacent cylindrical walls through edges 52.In one preferred example of the construction of tank 10, localizedregions 80, where the cylindrical walls 30 connect to each other, may beconstructed of a higher gage wall thickness. Similarly the remainder ofthe cylindrical walls 30 may be constructed of lower gage plating. Thismay be accomplished through tailor-welded blanks or other manufacture orassembly methods known by those skilled in the art.

In one preferred example shown in FIG. 1, eight end caps 60 are used tosealingly close the eight corners of the cubeshaped tank 10. End caps 60are spherical in shape and complimentary to the shape and orientation ofthe three adjacent cylindrical walls 30, namely, two horizontalcylindrical walls 46 and a vertical cylindrical wall 34. In thisconfiguration, the cylindrical walls 30 form a tank side opening 64 oneach of the six sides of tank 10. One or more entry ports (not shown) toaccess the interior storage chamber 66 may be used to efficiently fill,extract and monitor the tank contents.

Referring to FIG. 4, an alternate example of the outer shell of tank 10is shown. In this example, each of the alternate cylindrical walls 70includes corner portions 74 eliminating the need for end caps 60 shownin FIG. 1.

Referring to FIG. 5, tank 10 includes an internal cross brace 84.Internal cross brace 84 generally includes six brackets 98 angularlyorientated with respect to one another for preferable connection to eachof the six sides of tank 10 defined by cylindrical walls 30 as morefully described below. The two vertical oriented brackets 98 form acolumn 100 having an upper end 104 and lower end 108 defining a firstaxis 110. Brackets 98 forms a first side brace 112 defining a secondaxis 118 and a second side brace 114 defining a third axis 120. Thefirst, second and third axes meet at a center point (not shown). In apreferred example, the center point is positioned at approximately thecenter of gravity of the tank 10. Internal cross brace 84 is positionedbetween the six sides of tank 10 exterior to the internal storagechamber 66 containing the preferred fluid. The internal cross brace 84can be either tubular or a built up I-beam cross section (not shown).

Internal cross brace 84, and more particularly the four ends 116 on thefirst side brace 112 and second side brace 114 are connected tocylindrical walls 30 at the side openings 64 on each of the four sides,and top and bottom as best seen in FIG. 5. The rigid structuralconnections between each cylindrical wall 30 and internal cross brace 84provide a significantly more robust, structurally reinforced tank 10over prior tanks.

In a preferred example of materials for exemplary tank 10 shown in FIGS.1-3 and 5, cylindrical walls 30, end caps 60, and internal cross brace84 are all manufactured from nickel steel and have varying gage orthickness which is dependent upon the location of the plating, size andanticipated contents of the tank to suit the anticipated stresses in theplating or tank components. The respective components may be connectedtogether through continuous seam welds along all connecting joints forstrength and sealability of the tank. It is understood that differentmaterials, gages and methods of connection known by those skilled in theart may be used.

In an exemplary design as generally shown in FIGS. 1 and 2 with aninternal cross brace substantially as shown in FIG. 5, a suitableconstruction of a tank 10 may have the following characteristics. For avery large tank, for example an ultra-large LNG ocean carrier, a tankmeasuring approximately 36.6 meters each in length, width and height maybe used. The tank may be manufactured from nickel steel with a modulusof 210,000 MPa and a poison ratio of 0.3. Other materials may be used toform tank 10 including aluminum or selected steels. The contents may beliquid natural gas (LNG) having a specific gravity of 0.5 occupyingapproximately 95% of the tank 10 usable volume. In this example,analytical testing indicated areas of higher stress in the tank 10 atthe joints of the cylindrical walls 30 and region 80 of the cylindricalwalls 34 and 40 due to hydrostatic pressure loads on the tank.

In a preferred alternate example of tank 10, as best seen in FIGS. 2 and6-13, alternate tank 10 design includes an alternate cross brace 122 andside reinforcements 162. This alternate design discloses exemplary waysfor increasing the stress capabilities of the tank and connecting theinternal cross brace to an exemplary carrier hull structure. Referringto FIGS. 2 and 6, the alternate tank 10 includes twelve substantiallyidentical cylindrical walls 30 and end caps 60 as previously described.The alternate cross brace 122 comprises of a column 124 including afirst wall 126 and second wall 128 positioned approximatelyperpendicular to one another defining a first axis 110. Cross brace 122further includes a base 132 and base reinforcements 136 connected to thelower portion of column 124. Internal cross brace 122 further includesan alternate first brace 137 and a alternate second brace 138 defining asecond axis 118 and a third axis 120 respectively. The first, second andthird axes converge at a center point as previously described.

In the preferred example, each of the first 137 and second 138 bracesinclude top and bottom plate 140 and an inner wall 142 as generallyshown. Inner wall 142 may form two separate inner walls as shown.

In a preferred example, each of the first 137 and second 138 braces mayinclude an extension 150 extending axially outward from inner wall 142along second 118 and third 120 axes. Extensions 150 may each include apair of side walls 154 and top and bottom plates 155 extending axiallyoutward from inner wall 142 terminating at ends 158. As shown in FIGS. 6and 9, extension 150 may project slightly beyond tank side 20 forconnection of tank 10 to the inner walls of a cargo hold as furtherdescribed below.

In a preferred examples shown in FIGS. 6, 7 and 9, on each of the foursides 20 of tank 10, four alternate side reinforcements 162 are rigidlyattached to extensions 150 and project axially and radially outward fromsecond 118 and third 120 axes to substantially compliment the curvedouter surfaces of the cylindrical walls 30 as best seen in FIG. 7. Base132 of column 124 and reinforcements 136 serve to reinforce the bottom18 of tank 10.

Referring to FIG. 8, alternate tank 10 may include a base plate 170 usedto structurally connect tank 10 to the floor or hull of a cargo hold ina ocean carrier or other transportation device. In the example, crossbrace base column 124, base 132 and base reinforcements 136 are rigidlyconnected to base plate 170. These structures, along with sidereinforcements 162 on bottom 18, provide vertical and lateral support oftank bottom 18 and tank 10 in an exemplary cargo hold of a large LNGocean carrier.

Referring to FIGS. 7, 9-12 an alternate internal cross brace 122 sideextension 190 is shown differing from extensions 150 shown in FIG. 6. Inthe example, alternate side extensions 190 include a bevel 196preferably facing toward the bottom 18 of the tank 10 and are rigidlyconnected to end reinforcements 162 as previously described. Alternateside extensions 190 are preferably located in a slot 203 in cargo holdbulkhead 200 defined by bulkhead sides 202, angled support surface 204and hull side 208. Bulkhead 200, sides 202, and an angled supportsurface 204, allow the tank lateral extensions 190 to slide down thebulkhead sloped surface 204 (gap shown between 196 and 204 for purposesof illustration only) to accommodate any reduction in tank size due tothermal contraction, for example when cold fluids are loaded in to thetank. A vertical locking plate (not shown) may be positioned aboveextensions 190 in slot 203 to prevent vertical movement of extension 190once installed. Alternatively, extensions 190 may be securely attachedto the bulkheads or hull.

Referring to FIG. 14, an alternate side extension of internal crossbrace 122 is shown. In the example, walls 154, as shown in FIG. 6, areillustrated. In addition, a reinforcement 160 is added axially extendingfrom end 144 to attach to a hull or cargo hold bulkhead as previouslydescribed.

Referring to FIG. 15, an alternate internal cross brace 214 isillustrated. Alternate cross brace 214 preferably includes a column 216,a first side brace 220 and a second side brace 222. Similar to FIG. 6,cross brace 214 includes first 120, second 118 and third 120 axes. Asgenerally illustrated, cross brace 214 includes a general I-beamconstruction and connects to the six sides of the tank 10 (not shown) ina similar method as previously described. Cross brace 214 preferablyincludes several reinforcement gussets 226 (six shown in FIG. 15) andplates 230 (six shown) to reinforce the I-beam column, side braces andcross brace as generally shown. Cross brace 214 may further connect tothe hull or bulkheads of a transportation vehicle in a manner as furtherdescribed below

Referring to FIGS. 10-13, tank 10 in an exemplary use in a large LNGcarrier, may be positioned in a cargo hold or cargo bay area 206 of acarrier vessel 198 or other transportation vehicle. In the preferredexample, tank 10 is pre-fabricated and lowered by crane into, or isintegrally built into, a cargo hold 206. Tank 10 is vertically supportedby base plate 170 which rests on the cargo floor. Cross brace sideextensions 190, including preferred beveled 196, are positioned betweenbulkhead sides 202 and placed in supporting contact with bulkheadsurface 204 to lock the tank in a lateral position even as the tankoverall dimensions vary with varying cargo temperature. This support andsecuring design substantially eliminates the need for any mechanicalconnection. In this position, tank 10 is supported vertically andlaterally in cargo hold 206 for receipt and containment of a solid orfluid, for example LNG, for transportation over land or sea. Thestructural container tank 10 may be filled with, for example, LNG in arange from empty up to about 95 percent of the capacity of internalstorage chamber 66.

The tank 10 may be filled with, for example, LNG to a capacity of about95 percent of the internal storage chamber 66. As shown in the chartbelow, the volumetric efficiency of a tank 10 design (the CDTS) iscompared with prior tank designs and a proposed PRISM membrane tanksystem (Nobel 2005). Comparing the tanks to a solid cube of 49,108 cubicmeters, the respective volumes and efficiencies are shown.

TABLE 1 COMPARISON OF TANK VOLUMETRIC EFFICENCY Tank Type VolumeEfficiency Prismatic Self-Standing 46,162 0.94 Membrane 43,706 0.88Membrane PRISM 38,304 0.78 CDTS 40,000 0.8145 Sphere 25,713 0.5236

The table shows that the tank 10 (CDTS) is 60% more efficient than acomparable spherical tank and an improvement over the PRISM tank design.

Further, use of a large marine carrier or ship cargo space was alsocompared. The below table shows the cargo hold space required by each ofthe below tank designs compared for a 138,000 and 400,000 cubic metercarrier. The numbers in parentheses show the percentage comparison witha membrane tank-type lining system.

TABLE 2 COMPARISON OF HOLD SPACE REQUIRED BY PRISMATIC, MEMBRANE,SPHEREICAL AND CDTS Depth Space Length Breadth To Cover Usage CAPACITY138,000 m³ Prismatic Self Standing 176 (95) 44 (100) 35 (103) 0.51 (106)Membrane Original 186 (100) 44 (100) 34 (100) 0.48 (100) Spherical 192(103) 48 (109) 43 (126) 0.35 (73) CDTS 168 (90) 41 (93) 41 (121) 0.49(102) CAPACITY 400,000 m³ Prismatic Self Standing 240 (94) 64 (100) 49(102) 0.53 (104) Membrane Original 255 (100) 64 (100) 48 (100) 0.51(100) Spherical 285 (138) 67 (105) 57 (119) 0.37 (73) CDTS 230 (94) 58(91) 58 (121) 0.52 (102)

The table shows that there are significant size reductions and anincrease in percentage of use attainable in a large marine carrier usingtank 10 over certain tank systems.

In a preferred example and method of fabrication, the respectivecomponents of alternate tank 10 shown in FIGS. 6-13, are preferablyfabricated from nickel steel from substantially varying gage suitablefor the application and are seam welded as previously described. It isunderstood that tank 10 maybe fabricated in different sizes, and befabricated and assembled using alternate material and attachmenttechniques suitable for the particular contents and application.

The tank 10 includes numerous other advantages over prior tanks.Exemplary advantages of tank 10 include: flexibility on the amount offluid contained ranging from about 5 to about 95 percent of the tankcapacity; there is no need to stage the cargo hold to apply insulationand lining to the cargo hold; there is no need for significant weldingof the insulation and lining securing strips and the lining onboard aship; the tank 10 can be installed in one piece at the most efficienttime in the ship production process; tank 10 can be constructed ofdifferent materials and is modular in design; tank 10 can be produced atmany ship and transportation vehicle build sites using conventionaltools; tank 10 can be leak tested before installation in a ship ortransportation vehicle; tank 10 is not subject to the level of damagefrom dropped items as compared to membrane tank containment systems andtank 10 requires a smaller base support “foot print” compared tospherical tanks circumferential skirts. Other advantages known by thoseskilled in the art may be achieved.

While the invention has been described in connection with what ispresently considered to be the most practical and preferred embodiment,it is to be understood that the invention is not to be limited to thedisclosed embodiments but, on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims, which scope is to be accorded the broadestinterpretation so as to encompass all such modifications and equivalentstructures as is permitted under the law.

1. A storage tank comprising: an outer shell defining six interconnectedtank sides defining an interior storage chamber; a cross bracepositioned between the six sides and interconnecting at least four ofthe six sides.
 2. The storage tank of claim 1 wherein the outer shell iscubical in shape and comprises twelve substantially identicalcylindrically-shaped walls that each connect to the cross brace and fourof the adjacent cylindrical walls.
 3. The tank of claim 2 furthercomprising eight spherical end caps, each end cap positioned at one ofeight corners of the cubical tank sealingly connecting to three of theadjacent cylindrical side walls.
 4. The tank of claim 1 wherein thecross brace further comprises a column connected to two opposing sidesof the tank defining a top side and bottom side of the tank, the crossbrace further having a first and a second side bracket connected to thecolumn and angularly positioned with respect to one another, the columnand the first and second side brackets each connecting to a different ofthe six sides of the outer shell.
 5. The tank of claim 4 furthercomprising four side extensions, each extension extending axiallyoutward from one of the cross brace side brackets for connection to abulkhead of a ship or transportation vehicle.
 6. An improved cubicstorage tank for use in a ship or transportation vehicle, the storagetank including twelve interconnected cylindrical walls and eightspherical end caps defining six sides of the cubic tank and an interiorstorage chamber, the improved storage tank comprising: a cross bracepositioned between the six sides and interconnecting all six sides ofthe cubic tank.
 7. The improved tank of claim 6 wherein the cross bracefurther comprises a column connecting two of the six sides defining atop side and a bottom side of the tank, and a first and a second sidebrace angularly positioned relative to one another and connected to thecolumn and adjacent sides of the tank.
 8. The improved tank of claim 7wherein each side brace includes a top plate, a bottom plate and aninner wall.
 9. The improved tank of claim 7 further comprising a baseplate connecting to a lower portion of the cross brace column forconnection of the tank at the bottom side to a bulkhead of atransportation vehicle.
 10. The improved tank of claim 7 wherein atleast two of the side braces includes a brace extension extendingaxially outward from the tank side for connection of the tank to anadjacent bulkhead of a transportation vehicle.
 11. The improved tank ofclaim 10 wherein each extension includes four side reinforcementsextending axially and radially outward from the side brace andconnecting to an adjacent cylindrical wall.
 12. The improved tank ofclaim 9 wherein at least one side brace comprises at least two sideextensions on opposing ends, each extension including a beveled surfacefor lateral supporting connection of the tank to the bulkhead.
 13. Amethod of fabricating a cubic storage tank comprising the steps of:providing twelve substantially identical cylindrical wallsinterconnecting to one another at their edges defining six sides of thetank and an interior storage chamber; and providing a cross bracepositioned between the six sides and connecting to each of the sixsides.
 14. The method of claim 13 further comprising the step ofproviding eight spherically shaped end caps, each end cap attached tothree adjacent cylindrical walls to form a sealed tank for the storageof fluids.
 15. The method of claim 13 further comprising the step ofproviding four extensions connected to the cross brace for supportingthe tank on bulkheads in a ship or transportation vehicle.
 16. Themethod of claim 15 further comprising the step of providing four sidereinforcements extending axially and radially outward from the crossbrace and connecting to an adjacent cylindrical wall.
 17. The method ofclaim 13 further comprising the step of filling the tank interiorstorage chamber with a fluid.